Suvastu of the Aryan and the present day river Swat commences at Kalam with the confluence of Ushu and Utror Rivers and flows for about 160 kilometer across the valley up to Chakdara. The total length of the River is 250 kilometers from Kalam to River Kabul near Charsadda. Many large and small tributaries like Gahil, Mankial, Daral, Chail, Barwai, Arnowai and Jambil and Marghazar streams join the river along its course. A number of streams in the lower Swat, Swat Ranrizai and Adinzai also contribute to the river. The river with its tributaries forms the drainage basin for the valley.
River Swat flows with a higher speed in a narrow gorge with an average width of 35-40m, from Kalam to Madyan; the narrow course of the river continues up to Thalapand (Baghderai). Downstream the river may spreads up to 400m. In the extreme south of the valley, the meandering river once again enters into a narrow gorge and joins Panjkora River at Qalangi. There is a single high flow season from May to August. The variation in the wet season flow' and the winter flow' is striking. A rapid rise in temperature may increase the flow of the river due to melting snow on the mountains. Before joining River Kabul it I drains about 14,000 square kilometers area up to Munda Headworks.
The drain area comprises rugged mountains varying in heights from 600m to more than 6,000m with a steady general rise from south to north. The bed slopes of the river vary from 21m/km at Kalam to 4m/km at Munda Headwork. Two main canals, Upper Swat and Lower Swat canal have been dug out during the last century for irrigation of Peshawar valley plains south of Malakand pass and for power generation at Jabanr and Dargai.
The whole fresh water network of the valley can be divided into the Monsoon Excluded Splashing River Ecology (MESRE) and the Monsoon Prevailing Sluggish River Ecology (MPSRE). The MESRE, restricted to Swat Kohistan is represented by the torrent cold water. Trout prefer the rushing cold water ecosystem like that in Kohistan. It is therefore referred to as the trout ecology. The MPSRE that spreads over the river in the rest of the valley, particularly in the lower Swat, is characterized by cold water with rather sluggish movement. This ecosystem is predominantly occupied by Schizothorax associated fish species and is not visited by the Trout. It can therefore, be referred to as non-trout ecology.
River Swat plays an important role in the economic life of the valley. Its aesthetic value can never beunderestimated. The River is one of the main sources of tourist attraction and a source of recreation for the local people. The pleasant climate of the valley and its rich fertility is also mainly due to the River. It provides water for irrigation and domestic use and is a habitat for, beside other flora and fauna, a number of fish species and waterfowl. River Khialay and Jindai in District Charsada are the two main offshoots of River Swat. It is diverted near Batkhella for power generation and irrigation. The upper Swat canal flows under Malakand through Benton tunnel. Below Dargai the upper Swat canal is divided into two branches, one supplying Charsada and the other Swabai and Mardan'.